Inductive components and electronic devices using the same

ABSTRACT

An inductive component in which a large enough inductance is obtainable even when the size is made smaller and the profile is made lower and electronic devices using the inductive component are provided. The inductive component includes a coil, a through hole inside the coil, and a multilayer magnetic layer, and the multilayer magnetic layer is disposed on the top and the bottom surfaces of the coil and the inner wall of the through hole.

THIS APPLICATION IS A U.S. NATIONAL PHASE APPLICATION OF PCTINTERNATIONAL APPLICATION PCT/JP2003/013894.

TECHNICAL FIELD

The present invention relates to inductive components for use in powersupply circuits of portable telephones and the like and to electronicdevices using the inductive components.

BACKGROUND ART

Referring to FIG. 11, a description of power supply circuits for use inportable telephones and the like will be given.

Using a voltage of 4V, for example, of battery 101 as the input voltage,it is possible to obtain an output voltage of 2V. Here, coil 102 iscalled a choke coil. By putting coil 102 in the circuit, a stable outputvoltage can be obtained. Also, in order to more stabilize the outputvoltage, it is necessary to increase the inductance of coil 102. In thisway, the power supply circuit of FIG. 11 is capable of supplying a DCoutput voltage which is more stabilized.

Generally, in order to increase the inductance of coil 102, it isnecessary to increase the cross-sectional area of the core of coil 102and to increase the number of turns. This presents a problem of a needto increase the volume of coil 102. On the other hand, in associationwith the requirement in recent years for a smaller size and lowerprofile design of portable telephones, there is an increasingly strongerrequirement for smaller size and lower profile design of coils for thepower supply circuit of portable telephones. For example, coil 102 withan area smaller than 5 mm×5 mm and a thickness of less than 1 mm isbeing required. Furthermore, the switching frequency has increased fromseveral hundred kHz to several tens of MHz. In association with such atrend toward higher frequencies of the switching frequency, reduction inthe core loss is being required. Also, as devices have come to be usedat lower voltages and higher currents, there is a case in which amaximum current greater than 0.1 A flows in a coil having a small sizeand a low profile. For this reason, it is necessary to reduce theresistance of the coil to a lower value.

Japanese Laid-Open Patent Application No. H09-223636 (page 3, FIG. 1)discloses a method for solving these issues.

Referring to FIG. 12, a description of a conventional inductivecomponent will be given. Multilayer magnetic films 112 support coil 111in a manner sandwiching with the intervention of interlayer insulatinglayer 115. And through-hole sections (hereinafter “THP”) 114 areprovided on the sides and in the center of coil 111. Furthermore, THP114 is filled with magnetic material 113. Also, as coil 111 is formed bywinding a strip of high electric-conductivity materials such as copper,coil 111 can be made thin. However, the above-mentioned coil with aconventional configuration suffered a problem that the inductance couldnot be increased to a high enough value. Furthermore, as magnetic layer113 is formed inside THP 114, the cross-sectional area of magnetic layer113 becomes large. When a current is fed through coil 111, a magneticflux that vertically penetrates THP 114 is generated, and an eddycurrent is generated in the horizontal plane of magnetic layer 113. Asthe cross-sectional area of magnetic layer 113 is large, the eddycurrent is large.

As a result, the magnetic flux that vertically penetrates THP 114 isreduced.

Consequently, the inductance of the coil cannot be increased. On theother hand, by using a magnetic material having a higher specificresistance, the eddy current can be reduced to a certain extent.However, when the switching frequency increases from several hundred kHzto several tens of MHz, a satisfactory effect of eddy current reductioncannot be obtained. Also, when the diameter of a through hole is 1 mm orsmaller, and the depth is 0.1 mm or greater and 1 mm or smaller, forexample, it is difficult to fill or dispose a magnetic material into theTHP by sputtering or vapor deposition because of difficulties in qualityand productivity. The present invention addresses these issues andprovides inductive components with which sufficient inductance isobtainable even when designed with a smaller size and a lower profile,and electronic devices that use those inductive components.

SUMMARY OF THE INVENTION

The present invention provides an inductive component including a coil,a through hole part and a multilayer magnetic layer, wherein themultilayer magnetic layer is disposed on the inner wall of the throughhole part and the top and the bottom surfaces of the coil.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an inductive component of Embodiment 1of the present invention.

FIG. 2 is a cross-sectional view of an inductive component of Embodiment1 of the present invention.

FIG. 3 is an enlarged cross-sectional view of THP of Embodiment 1 of thepresent invention.

FIG. 4 is an enlarged cross-sectional view of the top surface of a coilof Embodiment 1 of the present invention.

FIG. 5 is an enlarged cross-sectional view of the inner wall of THP ofEmbodiment 1 of the present invention.

FIG. 6 is an enlarged cross-sectional view of the inner wall of THP ofEmbodiment 2 of the present invention.

FIG. 7 is an enlarged cross-sectional view of a corner section of amultilayer magnetic layer of Embodiment 3 of the present invention.

FIG. 8 is an enlarged cross-sectional view of the top section of THP ofEmbodiment 4 of the present invention.

FIG. 9 is a perspective view of a multilayer magnetic layer ofEmbodiment 5 of the present invention.

FIG. 10 is an enlarged perspective view of the inner wall of THP ofEmbodiment 6 of the present invention.

FIG. 11 is a circuit diagram of a power supply circuit used in aportable telephone.

FIG. 12 is a cross-sectional view of a conventional inductive component.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT FOR CARRYING OUT THEINVENTION

Referring to drawings, a description of preferred embodiments of thepresent invention will be given in the following. The drawings areschematic diagrams and do not represent dimensionally correct positions.

(Embodiment 1)

FIG. 1 and FIG. 2 illustrate an inductive component of Embodiment 1. InFIG. 2, coil 21 and through-hole electrode 50 are formed with a platedhigh-conductivity material such as copper and silver. Needless to say,coil 21 may be formed with a copper wire. THP 22 is formed in the centerof coil 21. Depending on the occasion, THP 22 may be formed on theoutside of coil 21. While the thickness of coil 21 differs depending onthe device in which it is to be used, at least a thickness of 10 μm isnecessary in order to cope with a large current. Also, the coil on theupper level of coil 21 is spirally wound toward THP 22 starting fromterminal 23 located on one of the sides of the inductive component. Thecoil then moves to the lower level at the center and is spirally woundtoward terminal 24 located at the other side of the inductive componentstarting from through-hole electrode 50. Here, the directions of windingof the upper level and lower level coils of coil 21 are the same.Accordingly, when a current is fed from terminal 23, it spirally flowsfrom a side of the inductive component toward the center through theupper level of coil 21. The current further flows from the upper levelto the lower level, and spirally flows through the lower level of coil21 from the center of the inductive component toward the side, and isput out from terminal 24. Coil 21 may not necessarily be of two levelsand may be of one level or three or more levels. Coil 21 is buriedinside coil insulating material 25. Coil insulating material 25 preventscoil 21 from short-circuiting.

Next, multilayer magnetic layer (hereinafter “MLM”) 30 is disposed onthe top surface of coil 21 and the inner wall of THP 22 is formed at thesame time. Here, MLM 3O consists of magnetic layers 26 and insulatinglayers 29. Furthermore, MLM 30 is also formed on the bottom surface ofcoil 21. Insulating material 27 is formed in a manner covering MLM 30.That is, it covers MLM 30 on the top and bottom surfaces of coil 21 aswell as MLM 30 inside THP 22. Insulating material 27 is also filled inthe space formed by MLM 30 inside THP22. Insulating material 27 isprovided in order to prevent short-circuit when mounting the inductivecomponent on an electronic component in a state in which MLM 30 isexposed.

While FIG. 2 illustrates a state in which the space formed by MLM 30inside THP22 is totally filled with insulating material 27, it is notnecessary to totally fill the space. However, when sucking and mountingthe inductive component on a substrate, it is more preferable thatinsulating material 27 be totally filling the space formed by MLM 30inside THP 22. Also, as insulating material 27, an organic resin such asepoxy resin, silicone resin, or acrylic resin is preferable.

In FIG. 2, although all of MLM 30 is formed into an integrated unit, itneed not necessarily be integrated. However, in order not to produce amagnetic gap, it is preferable to form a continuous magnetic layer atcorner section 71 of THP 22 where magnetic fluxes tend to concentratemost intensely. By forming the magnetic layer in this way, leakage fluxcan be made smaller and inductance can be made larger. By the way, amagnetic material may be disposed on MLM 30 inside THP 22. When doingthis, it is more preferable that the magnetic material be brought intoas intimate contact as possible in order not to produce a magnetic gap.Also, the magnetic material is made of at least one material selectedfrom the group consisting of a ferrite magnetic material, a composite offerrite magnetic powder and an insulating resin, and a composite ofmetal magnetic powder and an insulating resin. With this configuration,superior reliability is obtainable as superior insulation can beobtained and possibility of occurrence of short-circuit in the circuitcan be reduced even without insulating material 27.

FIG. 3 is an enlarged cross-sectional view of THP 22. Platingunder-layer 28 is provided in order to form MLM 30 on coil insulatingmaterial 25. That is, it is provided to facilitate formation of magneticlayer 26 on plating under-layer 28 by electroplating. Platingunder-layer 28 is formed by electroless plating, for example, andcopper, nickel or metal magnetic layer having good conductivity ispreferably used.

MLM 30 is formed in a manner such that insulating layer 29 interposesmagnetic layers 26 as illustrated in FIG. 4. MLM 30 is formed asfollows. First, magnetic layer 26 is formed by electroplating on platingunder-layer 28 followed by forming insulating layer 29 on top of it byelectroplating or electrodeposition. Furthermore, thin MLM 30 can beformed by succeedingly forming a magnetic layer, an insulating layer,and a magnetic layer. In FIG. 4, MLM 30 has three layers. However, thenumber of the magnetic layers may be one or two, or four or more. Samething applies to the structure of MLM 30 to be disposed under the coil.Furthermore, when forming MLM 30, in order to facilitate formation of amagnetic layer by electroplating, an under layer similar to platingunder-layer 28 may be provided between the insulating layer and themagnetic layer. The magnetic layer may be formed by electroplating.Needless to say, similar advantage is obtainable by laminating MLM 30 bya method other than what is described above so far as the structure isthe same.

MLM 30 is formed in a manner such that the main component of at leastone of the layers of MLM 30 includes at least one element selected fromthe group consisting of Fe, Ni, and Co. In this way, a magnetic layerhaving superior magnetic properties for satisfying requirement for ahigh saturation magnetic flux density and a high magnetic permeabilityto cope with a large current can be obtained, and a high inductance canbe realized. Thickness of each of the magnetic layers differs dependingon the switching frequency. Assuming a switching frequency range ofseveral hundred kHz to several tens of MHz, the thickness is preferablybetween 1 μm to 50 μm. Also, while the thickness of each insulatinglayer differs depending on the specific resistance, the preferable rangeis from 0.01 μm to 5 μm. While the specific resistance of the insulatinglayer is the higher the better, the insulating layer is effective so faras the ratio of its specific resistance to that of the magnetic layer is10³ or higher. As the material for the insulating layer, organic resinsor inorganic materials such as metal oxides are preferable. A mixture ofthese materials is also good.

FIG. 5 is an enlarged cross-sectional view of the inner wall of THP 22.As shown in FIG. 5, MLM 30 is formed in a manner such that insulatinglayer 29 interposes between magnetic layers 26. MLM 30 is formed asdescribed below. First, magnetic layer 26 is formed by electroplating ontop of plating under-layer 28 followed by formation of insulating layer29 by electroplating or electrodeposition. MLM 30 is formed by furthersequentially forming a magnetic layer, an insulating layer, and amagnetic layer on top of insulating layer 29. In this way, thecross-sectional area of the magnetic layer per layer of MLM 30 issufficiently minimized by electroplating. In FIG. 5, MLM 30 has threelayers. However, the number of the magnetic layers may be one or two, orfour or more.

Furthermore, in forming MLM 30, an under layer similar to platingunder-layer 28 may be provided between the insulating layer and themagnetic layer in order to facilitate the formation of magnetic layer 26by electroplating. The magnetic layer may also be formed by electrolessplating. Needless to say, when MLM 30 is formed by a method other thanthe above described, the same advantage is obtainable so far as thestructure is the same. MLM 30 is formed in a manner such that the maincomponent of at least one layer of MLM 30 includes at least one elementselected from the group consisting of Fe, Ni, and Co. In this way, MLM30 having superior magnetic properties for satisfying a requirement fora high saturation magnetic flux density and a high magnetic permeabilityto cope with a large current can be obtained. At the same time, a highinductance can be realized. Preferable thickness of each of the magneticlayers differs depending on the switching frequency. Assuming aswitching frequency range of several hundred kHz to several tens of MHz,the thickness is preferably between 1 μm to 50 μm. While the thicknessper layer of the insulating layers differs depending on the specificresistance, the preferable range is from 0.01 μm to 5 μm.

Also, while the specific resistance of the insulating layers is thehigher the better, the insulating layer is effective so far as the ratioof its specific resistance to that of the magnetic layer is 10³ orhigher. As the material for the insulating layers, organic resins orinorganic materials such as metal oxides are preferable.

Furthermore, a mixture of these materials is also good. A description ofoperation of an inductive component having above configuration will nowbe given in the following. Coil 21 is spirally wound with highregularity and has a two-level structure with the same direction ofwinding. For this reason, when a current is fed to coil 21, a strongmagnetic flux is obtainable enabling an increase in the inductance ofthe inductive component. Accordingly, an inductive component having alarge enough inductance is obtainable even when the size is made smallerand the profile is made lower. Also, coil 21 is formed by copper platingand the like and its cross-section is a square. The advantage of squarecross-section of coil 21 lies in that the cross-sectional area can bemade greater than that obtainable when the cross-section of coil 21 isround. As a result, coil 21 with a low electric resistance, a smallsize, and a low profile is obtainable.

By using a coil having a high space factor like this, copper lossgenerated in the coil can also be reduced. When a current is fed to aninductive component, a magnetic flux is generated in the inductivecomponent. Magnetic fluxes are also generated in the direction of theplane of MLM 30 disposed on the top and the bottom surfaces of coil 21.A magnetic flux is also generated in the direction of the plane of MLM30 formed on the inner wall of THP 22. Because of these fluxes, an eddycurrent is generated in the direction of the thickness of MLM 30. Asthis eddy current reduces the magnetic flux generated in the directionof the plane of MLM 30, the inductance of the inductive componentdecreases.

Also, the eddy current generated in the direction of thickness of MLM 30causes heat generation from the inductive component. However, in theinductive component of this embodiment, MLM 30's are formed on the topand the bottom surfaces of coil 21. As a result, the cross-sectionalarea per layer of MLM 30 in the direction of the thickness becomes smallenough relative to the eddy current. Furthermore, as MLM 30 is formed onthe inner wall of THP 22, the cross-sectional area per layer of MLM 30in the direction of the thickness is made small enough. As the eddycurrent generated in the direction of the thickness of MLM 30 can besuppressed, reduction of the flux generated in the direction of theplane of MLM 30 can be prevented. Inductance of the inductive componentcan be made large in this way. Also, heat generation from the inductivecomponent can be suppressed.

On the other hand, it is difficult to form MLM 30 by sputtering or vapordeposition on the inner wall of THP 22 of which the diameter is 1 mm orsmaller and the depth is 0.1 mm or greater and 1 mm or smaller, forexample. Formation by plating is most preferable. In this way, aninductive component having a large enough inductance is obtainable. As alarge enough inductance is obtainable with the inductive component ofthis embodiment even when designed with a smaller size and a lowerprofile as noted above, it can be mounted in various small electronicdevices such as portable telephones.

(Embodiment 2)

Referring to FIG. 6, a description of an inductive component inEmbodiment 2 will now be given. Basic structure of the inductivecomponent is the same as that of the inductive component ofEmbodiment 1. What is different from embodiment 1 is that thethicknesses of each of magnetic layers 26 that compose MLM 30 aredifferent. In FIG. 6, MLM 30 is formed in a manner such that each ofmagnetic layers 26 is separated by insulating layer 29. MLM 30 is formedas described below. First, magnetic layer 26 is formed by electroplatingon top of a plating under-layer followed by formation of insulatinglayer 29 by electroplating or electrodeposition. MLM 30 is completed byfurther sequentially forming a magnetic layer, an insulating layer, anda magnetic layer. In this way, the cross-sectional area per layer of themagnetic layers of MLM 30 is made small enough. Differently fromEmbodiment 1, MLM 30 to be formed on the inner wall of THP 22 of theinductive component in this Embodiment is formed in the following way.MLM 30 is formed in a manner such that the thickness of each of magneticlayers 26 that compose MLM 30 increases as magnetic layer 26 comescloser to the center of coil 21. In FIG. 6, though MLM 30 has threemagnetic layers, the number of layers may be two or four or more. Also,in forming MLM 30, an under layer similar to plating under-layer 28 maybe provided between an insulating layer and a magnetic layer tofacilitate formation.

A description of the operation of the inductive component as formedabove will now be given in the following. When a current is fed to coil21, a magnetic flux is generated. This magnetic flux creates a magneticcircuit primarily along the outer wall, the top surface, the bottomsurface, and the inner wall of THP 22 of coil 21. The magnetic flux ofthe outer side of the magnetic circuit is weaker as the magnetic pathlength is greater. The magnetic flux generated in the direction of theplane of MLM 30 formed on the inner wall of THP 22 shifts toward theoutside of the magnetic circuit formed by MLM 30 as the center of coil21 becomes nearer.

And, as the magnetic path length becomes greater, the magnetic fluxbecomes weaker. As a result, the flux penetrating MLM 30 formed on theinner wall of THP 22 becomes non-uniform. However, in this Embodiment,each of magnetic layers 26 of MLM 30 formed on the inner wall of THP 22is formed in a manner such that its thickness increases as the center ofcoil 21 becomes nearer. As a result, the magnetic resistances of each ofmagnetic layers 26 are unified. And the magnetic flux penetrating eachof magnetic layers 26 of MLM 30 in the direction of the plane will notbecome weaker as the center of coil 21 becomes nearer. As a result, themagnetic flux that penetrates MLM 30 formed on the inner wall of THP 22will become uniform thus reducing the leakage flux. As is set forthabove, in the inductive component of this Embodiment, the magnetic fluxthat penetrates MLM 30 formed on the inner wall of THP 22 of coil 21becomes uniform. As a result, the leakage flux can be reduced and alarger inductance can be obtained.

(Embodiment 3)

Next, a description of an inductive component in this Embodiment will begiven referring to FIG. 7. The basic structure of the inductivecomponent is the same as that of the inductive component ofEmbodiment 1. Difference lies in that the thicknesses of the magneticlayers of corner section 71 consisting of MLM 30 formed on the innerwall of THP 22 of coil 21 and MLM 30 disposed on the top and the bottomsurfaces of the coil are made thicker. In FIG. 7, corner section 71 isformed in a manner such that the thicknesses of magnetic layers of MLM30 become thicker. As a result, the cross-sectional area in thedirection of the thickness of MLM 30 at corner section 71 is madegreater than the cross-sectional area in the direction of thethicknesses of MLM 30 disposed on the top and the bottom surfaces ofcoil 21 and MLM 30 formed on the inner wall of THP 22.

A description of the operation of an inductive component having theabove configuration will now be given below. When a current is fed tocoil 21, a magnetic flux is generated. This magnetic flux forms amagnetic circuit primarily along the outer wall, the top surface, andthe bottom surface of coil 21, and the inner wall of THP 22.Furthermore, a magnetic flux is also generated in the direction of theplane of MLM 30. The magnetic flux in the direction of the plane of MLM30 is easy to leak from the magnetic circuit formed by MLM at cornersection 71 of MLM 30 of THP 22 where the magnetic flux concentrates mosteasily.

However, the inductive component in this Embodiment is formed in amanner such that the thicknesses of each of the magnetic layers of MLM30 at corner section 71 are greater. Accordingly, the cross-sectionalarea of MLM 30 in the direction of thickness is made greater at cornersection 71, and the magnetic resistance at corner 71 against themagnetic flux that penetrates MLM 30 in the direction of the planebecomes smaller. As a result, leakage from the magnetic circuit formedby MLM 30 at corner section 71 of the magnetic flux that penetrates MLM30 in the direction of the plane can be prevented.

Inductance of the inductive component can be increased in this way. Insummary, an inductive component having a large enough inductance isobtainable according to this Embodiment.

(Embodiment 4)

Next, a description of an inductive component in this Embodiment will begiven referring to FIG. 8. The basic structure of the inductivecomponent is the same as that of the inductive component inEmbodiment 1. However, difference lies in that a recess is provided oninsulating material 27 of at least either of the top and the bottomsurfaces of THP 22. FIG. 8 is an enlarged view of a vicinity of theupper part of THP 22 of the inductive component of this Embodiment. InFIG. 8, insulating material 27 is filled in the space formed by MLM 30inside THP 22. And a recess is provided on at least either of the topand the bottom surfaces of THP 22. As insulating material 27, an organicresin material such as epoxy resin, silicone resin, and acrylic resin ispreferable.

A description of the operation of the inductive component having theabove structure will be given below. When mounting the inductivecomponent of this Embodiment onto a power supply circuit board of anelectronic device such as a portable telephone, a finished inductivecomponent is sucked and mounted onto the circuit board. In this process,provision of a recess on at least either the top or the bottom surfaceof THP 22 of the inductive component facilitates suction. The depth ofthe recess is as required to facilitate suction and the shallower thebetter. By providing a recess, falling of the inductive component whilebeing sucked and transferred can be prevented. The inductive componentsof the first to the fourth Embodiments may be covered with a magneticmaterial, a metal plate, or a multilayer magnetic layer. Leakage fluxcan be further reduced by such an arrangement. In this case, a recessfor suction may be provided on these magnetic layers.

(Embodiment 5)

Next, referring to FIG. 9, a description will be given on an inductivecomponent of this Embodiment. While the basic structure of the inductivecomponent is the same as that of the inductive component of Embodiment1, difference lies in that slit 91 is provided in the direction of theplane of MLM 30.

Slit 91 is also provided in the direction of the plane of MLM 30disposed on the bottom surface of coil 21, shown in FIG. 2.

In FIG. 9, though four slits 91 are provided, the number may be one, twoor more. A description of the operation of an inductive component havingthe above structure will be given below. When a current is fed to coil21, magnetic fluxes are generated in the inductive component. Most ofthe magnetic fluxes are generated in the direction of the planes of MLM30 disposed on the top and the bottom surfaces of coil 21.

However, as the inductive component becomes smaller in size and lower inprofile, magnetic fluxes are also generated in the directions of thethicknesses of multilayer magnetic layers 30 disposed on the top and thebottom surface of coil 21. As these magnetic fluxes generate eddycurrents in the direction of the plane of MLM 30 disposed on the top andthe bottom surfaces, the inductance is reduced. And, the eddy currentgenerated in the direction of the thickness of MLM 30 causes heatgeneration from the inductive component. However, as the inductivecomponent of this Embodiment has slits 91 in the direction of the planeof MLM 30, the cross-sectional area of MLM 30 in the direction of theplane can be made small.

Consequently, the eddy current generated in the direction of the planeof MLM 30 disposed on the top and the bottom surfaces can be suppressed.In this way, the inductance of the inductive component can be increased.Also, heat generation from the inductive component can be suppressed.Accordingly, an inductive component having a large enough inductance isobtainable even when the size is made smaller and the profile is madelower. The inductive component of this Embodiment has slits 91 in thedirection of the plane of MLM 30 disposed on the top and the bottomsurfaces of coil 21. When plating under-layers 28 are to be formed onthe top and the bottom surfaces of coil 21, slits 91 are formed in thedirection of the plane of plating under-layers 28. As a result,cancellation of the magnetic flux generated in the direction of thethickness of plating under-layers 28 can be prevented. Such anarrangement is preferable as the inductance of the inductive componentcan be increased. Also, heat generation from the inductive component canbe suppressed. In this way, an inductive component having large enoughinductance is obtainable even when the size is made smaller and theprofile is made lower.

(Embodiment 6)

Referring to FIG. 10, a description of an inductive component of thisEmbodiment will now be given. The basic structure of the inductivecomponent is the same as that of the inductive component ofembodiment 1. Difference lies in that slit 92 is formed in the verticaldirection from the top to the bottom of MLM 30 formed on the inner wallof THP 22. The operation of an inductive component having this structurewill be given in the following. When a current is fed to coil 21,magnetic fluxes are generated in the inductive component. Most of themagnetic fluxes are generated in the top and the bottom surfaces of coil21 and in the direction of the plane of MLM 30 disposed on the innerwall of THP 22. Furthermore, a vertical magnetic flux is also generatedaround the center of an empty space formed by MLP 26 in the inner wallof THP 22. An eddy current is generated in the direction of cancelingthis magnetic flux, especially in the circumferential direction ofannular MLM 30 disposed on the inner wall of THP 22. As a result, theinductance decreases.

However, the inductive component of this Embodiment has slit 92 in thevertical direction of MLM 30 formed on the inner wall of THP 22.Accordingly, the eddy current in the circumferential direction can becut and the inductance of the inductive component can be increased.Also, heat generation from the inductive component can be suppressed.While a single vertical slit is provided in FIG. 10, needless to say,the number of slits may be two or more. Furthermore, it is preferable toprovide in the vertical direction a slit with a thinnest possiblethickness from the standpoint of obtaining a high inductance.

The width of the slit is in the range 0.01 to 50 μm, preferably 1 to 10μm. Also, the slit is formed by known methods such as masking-etchingmethod and laser-cut method.

In this way, an inductive component having a high enough inductance isobtainable even when the size is made smaller and the profile is madelower. By the way, even when a slit is provided in the lateral directionof MLM 30 formed on the inner wall of THP 22, it is not possible to cuteddy current in the circumferential direction of MLM 30 formed on theinner wall of THP 22.

INDUSTRIAL APPLICABILITY

The inductive components of the present invention have large enoughinductance even when the size is made smaller and the profile is madelower. Accordingly, they are most suitable as inductive components forelectronic devices that require smaller size and lower profile. They canbe used in power supply circuits of portable telephones, for example.

1. An inductive component comprising: an insulating layer: a coil buriedin the insulating layer having a top surface and a bottom surface; acenter portion formed from an insulating material; a multilayer magneticlayer wrapped around the center portion and comprising a plurality ofinsulating layers and a plurality of magnetic layers such that one isinterspersed with the other; and a magnetic material disposed on the topand the bottom surfaces of the coil.
 2. An inductive component accordingto claim 1, wherein the magnetic material is the multilayer magneticlayer.
 3. The inductive component of claim 1, wherein the magneticmaterial is at least one selected from the group consisting a ferritemagnetic material, a composite of ferrite magnetic powder and aninsulating resin, and a composite of metallic magnetic powder and aninsulating resin.
 4. The inductive component of claim 2, wherein aninsulating material is filled in a space formed by the multilayermagnetic layer disposed on the inner wall of the through hole.
 5. Theinductive component of claim 2, wherein the multilayer magnetic layer isformed by alternately laminating the magnetic layer and the insulatinglayer.
 6. The inductive component of claim 2, wherein the multilayermagnetic layer has at least one layer formed by plating.
 7. Theinductive component of claim 2, wherein the main component of themultilayer magnetic layer includes at least one element selected fromthe group consisting of Fe, Ni, and Co.
 8. The inductive component ofclaim 2, wherein the thickness of each of the magnetic layers thatcompose the multilayer magnetic layer formed on the inner wall of thethrough hole of the coil increases toward the center of the coil.
 9. Theinductive component of claim 2, wherein the multilayer magnetic layerformed on the inner wall of the through hole of the coil and themultilayer magnetic layer disposed on the top and the bottom surfaces ofthe coil are formed into an integral unit.
 10. The inductive componentof claim 9, wherein the thicknesses of magnetic layers of a cornersection comprising the multilayer magnetic layer formed on the innerwall of the through hole of the coil and the multilayer magnetic layerdisposed on the top and the bottom surfaces of the coil are madegreater.
 11. The inductive component of claim 4, wherein at least one ofthe top and the bottom surfaces of the insulating material has a recess.12. The inductive component of claim 2, wherein a slit is formed in thedirection of the plane of the multilayer magnetic layer disposed on thetop and the bottom surfaces of the coil.
 13. The inductive component ofclaim 2, wherein a slit is formed at least at one vertical position ofthe multilayer magnetic layer formed on the inner wall of the throughhole.
 14. The inductive component of claim 1, wherein the multilayermagnetic layer is formed by alternately laminating a magnetic layer andan insulating layer.
 15. The inductive component of claim 1, wherein themultilayer magnetic layer has at least one layer formed by plating. 16.The inductive component of claim 1, wherein the main component of themultilayer magnetic layer includes at least one element selected fromthe group consisting of Fe, Ni, and Co.
 17. The inductive component ofclaim 1, wherein the thickness of each of the magnetic layers thatcompose the multilayer magnetic layer formed on the inner wall of thethrough hole of the coil increases toward the center of the coil. 18.The inductive component of claim 1, wherein the multilayer magneticlayer formed on the inner wall of the through hole of the coil and themultilayer magnetic layer disposed on the top and the bottom surfaces ofthe coil are formed into an integral unit.
 19. The inductive componentof claim 14, wherein a slit is formed in the direction of the plane ofthe multilayer magnetic layer disposed on the top and the bottomsurfaces of the coil.
 20. An inductive component according to claim 1,wherein the inductive component is included in an electronic device. 21.An electronic device that uses an inductive component, the inductivecomponent comprising: an insulating layer; a coil buried in theinsulating layer having a top surface and a bottom surface; a centerportion formed from an insulating material; a multilayer magnetic layerwrapped around the center portion and comprising a plurality ofinsulating layers and a plurality of magnetic layers such that one isinterspersed with the other; and a magnetic material disposed on the topand the bottom surfaces of the coil.